First, it is necessary to understand what PNP and NPN mean. P represents positive and N represents negative. PNP indicates that the signal is usually at a high potential and turns negative when the signal arrives. NPN indicates that it is at a low potential under normal circumstances and outputs a high potential when the signal arrives. Proximity switches and photoelectric switches only have different detection circuits but the same output. As for PLC wiring, NPN is generally used more frequently. However, most Japanese PLCS come in Japanese type, international type, and general-purpose type. Most of the ones entering China are of global and general types. The NPN type can be used directly. The positive terminal of the power supply for proximity switches and photoelectric switches should be connected to the positive and negative terminals of the power supply, and the output should be connected to the input terminal of the PLC.

The input types of PLC are divided into drain type and source type. The former refers to positive signal input (PNP can be directly used), and the latter refers to negative signal input (NPN can be directly used). Otherwise, relay conversion must be used before input.

There are various types of sensors, but the most commonly used ones are two-wire and three-wire ones. The two-wire ones are connected in series with the load. Most three-wire ones are open-collector outputs, with the three wires being the positive and negative power supplies and the collector of the output transistor respectively. The NPN and PNP of a sensor are determined by the model of the output transistor. The load of NPN is connected between the positive power supply and the collector, while that of PNP is connected between the collector and the negative power supply. To determine the model of a sensor with a multimeter, it is necessary to first apply a load to it and then make a judgment based on its output voltage.

What is the fundamental difference between PNP and NPN sensors?

PNP and NPN type sensors actually utilize the saturation and cut-off of transistors to output two states, and they belong to switch-type sensors. However, the output signals are completely opposite, namely high level and low level. The NPN output is a low level of 0, and the PNP output is a high level of 1.

PNP and NPN type sensors (switching type) are classified into six categories:

1. NPN-NO (Normally Open Type)

2. NPN-NC (Normally Closed Type)

3. NPN-NC+NO (Normally Open and Normally Closed common Type)

4. PNP-NO (Normally Open Type)

5. PNP-NC (Normally Closed Type

6. PNP-NC+NO (Normally Open and Normally Closed Common Type)

PNP and NPN type sensors generally have three lead wires, namely the power line VCC, the 0V line, and the out signal output line.

1. PNP class

PNP refers to the connection of the signal output line out and the power line VCC when a signal is triggered, which is equivalent to a power line that outputs a high level.

For the PNP-NO type, when there is no signal trigger, the output line is suspended, meaning that the VCC power line and the out line are disconnected. When a signal is triggered, the same voltage as the VCC power line is emitted, that is, the out line is connected to the VCC power line, and a high-level VCC is output.

For the PNP-NC type, when there is no signal trigger, the same voltage as the VCC power line is emitted, that is, the out line is connected to the VCC power line, and a high-level VCC is output. When a signal is triggered, the output line is suspended, meaning that the VCC power line and the out line are disconnected.

For the PNP-NC+NO type, it is actually just an additional output line OUT, which can be selected as needed.

2. NPN class

NPN refers to the connection of the signal output line out and the 0v line when a signal is triggered, which is equivalent to outputting a low level, ov.

For the NPN-NO type, when there is no signal trigger, the output line is suspended, that is, the 0v line and the out line are disconnected. When a signal is triggered, the same voltage as OV is emitted, that is, the out line and the 0V line are connected to output a low-level OV.

For the NPN-NC type, when there is no signal trigger, the same voltage as the 0V line is emitted, that is, the out line is connected to the 0V line, and a low 0V level is output. When a signal is triggered, the output line is suspended, meaning the 0V line and the out line are disconnected.

For the NPN-NC+NO type, similar to the NPN-NC+NO type, it has an additional output line OUT and two output lines with inverting signals. The choice can be made as needed.

When connecting a 10 ~ 30VDC proximity switch to a PLC, how to determine whether to use PNP or NPN?

If the COM input of the PLC is connected to the negative terminal of the power supply, select NPN; if the COM terminal input of the PLC is connected to the positive terminal of the power supply, select PNP.

PNP and NPN type sensors actually utilize the saturation and cut-off of transistors to output two states, and they belong to switch-type sensors. However, the output signals are completely opposite, namely high level and low level. The PNP output is at a low level of 0, and the NPN output is at a high level of 1.

PNP and NPN type sensors (switching type) are classified into six categories:

1. NPN-NO (Normally Open Type)

2. NPN-NC (Normally Closed Type)

3. NPN-NC+NO (Normally Open and Normally Closed common Type)

4. PNP-NO (Normally Open Type)

5. PNP-NC (Normally Closed Type

6. PNP-NC+NO (Normally Open and Normally Closed Common Type)

PNP and NPN type sensors generally have three lead wires, namely the power line VCC, the 0V line, and the out signal output line.

1. NPN class

NPN refers to the connection between the signal output line out and the power line VCC when a signal is triggered, which is equivalent to a power line that outputs a high level.

For the NPN-NO type, when there is no signal trigger, the output line is suspended, meaning that the VCC power line and the out line are disconnected. When a signal is triggered, the same voltage as the VCC power line is emitted, that is, the out line is connected to the VCC power line, and a high-level VCC is output.

For the NPN-NC type, when there is no signal trigger, the same voltage as the VCC power line is emitted, that is, the out line is connected to the VCC power line, and a high-level VCC is output. When a signal is triggered, the output line is suspended, meaning that the VCC power line and the out line are disconnected.

For the NPN-NC+NO type, it's actually just an additional output line OUT. You can choose or eliminate it as needed.

2. PNP class

PNP refers to the situation where, when a signal is triggered, the signal output line out is connected to the 0v line, which is equivalent to outputting a low level, ov.

For the PNP-NO type, when there is no signal trigger, the output line is suspended, that is, the 0v line and the out line are disconnected. When a signal is triggered, the same voltage as OV is emitted, that is, the out line and the 0V line are connected to output a low-level OV.

For the PNP-NC type, when there is no signal trigger, the same voltage as the 0V line is emitted, that is, the out line is connected to the 0V line, and a low 0V level is output. When a signal is triggered, the output line is suspended, meaning the 0V line and the out line are disconnected.

For the PNP-NC+NO type, similar to the NPN-NC+NO type, it has an additional output line OUT and two output lines with inverting signals. The choice can be made as needed.

The type we usually use frequently is NPN, which stands for high-level effective state. PNP is rarely used.

First, locate the power supply terminal and output terminal of the proximity switch. If it is a two-wire system, there should be a +VDC terminal, an output terminal or a "-" terminal! For source-type input PLCS such as Modicon and Siemens (see which PLC you are using), you can connect the +24V sensor power supply that comes with the PLC to the +VDC terminal! The output terminal of the proximity switch can be connected to the input terminal of the PLC! For source-type input PLCS, once the proximity switch operates, the PLC input terminal will receive a DC voltage slightly less than that of the PLC sensor power supply, thus making the PLC switch input effective! For PLCS like Mitsubishi, since they receive leakage input, the power supply terminal of the proximity switch should be connected to the input terminal (such as X10), while the output (or the "-" terminal) should be connected to the power ground terminal. Once the proximity switch operates, the output of the proximity switch drops (or approaches the ground potential), making the PLC input effective!

The three-wire proximity switch must be connected to the positive power supply and ground terminal of the sensor!

The power supply of the sensor must be the same as that of the proximity switch or there should be a current forming a loop for it to work! Mitsubishi, however, doesn't need to make a difference because its switch input already comes with its own power supply!

It should be noted that some proximity switches, although two-wire type, have three wires, among which one is a shielded wire. They should be distinguished!

Summary: For the switch input circuits of PLCS. Personally, I think the PLCS from Mitsubishi in Japan are much better. They are even more practical and reliable than those from renowned brands like Siemens! The main reason is that Japanese PLCS such as Mitsubishi learned the technology from Europe and America and optimized the design, achieving:

1. It adopts a missed input. The input terminal is originally designed to trigger an open input when there is a short circuit to ground. It will not pose a threat to the power supply system, nor will it affect the normal operation of other input circuits due to power failure!

2. It adopts source input and is a common power supply input terminal. In practical engineering applications, there are often too many cables. You may not be able to ensure that the cables come into contact with each other or get damaged. Maybe the switch quantity lines of the common power supply will accidentally come into contact with the equipment ground, the casing, or other ground potentials. Therefore, the power supply circuit may be disconnected. It may cause damage to the power supply or blow out the fuse, thereby affecting the normal operation of other input circuits. Unless a fuse is added to each input loop... The application cost is relatively high and it is also prone to other malfunctions.